In general, as a method of supporting a powertrain for a vehicle, there are an inertial support method, a center support method, and a composite support method. At present, among these methods, the inertial support method, which is relatively excellent in respect to idle performance, is widely used, and the inertial support method uses a principal axis of inertia of an engine, and is classified into a four-point support method and a three-point support method based on the number of mounts.
Here, the four-point support method is a method in which an engine mount and a transmission mount are positioned at an upper end or a lateral side of a side member of a vehicle body, and front and rear roll stoppers are mounted on a sub frame.
In contrast, the three-point support method is a method in which an engine mount disposed at one side of an engine and a transmission mount disposed at one side of a transmission are mounted at an upper end or a lateral side of a side member of a vehicle body like the four-point support method, but a roll rod, instead of the front and rear roll stoppers, is mounted on a sub frame or a cross member.
Recently, in most instances, the inertial three-point support method is also applied and adopted by a high-torque engine for a medium-sized/large-sized vehicle, and an I-shaped sub frame type is widely adopted in order to reduce a weight of the vehicle. Accordingly, an importance of the three-point support method is emphasized, and it is necessary to develop the roll rod to be used. Further, the roll rod, which is used for the three-point support method, is used such that one side of the roll rod is fixed to the powertrain and the other side of the roll rod is fixed to the sub frame.
Meanwhile, the powertrain refers to a series of all devices, such as a clutch, a transmission, a final reduction gear device, and the like that transmit power generated by the engine to drive wheels, and a front bushing of the roll rod is fixed to the powertrain and serves to primarily reduce vibration.
Typically, a rear bushing of the roll rod more sensitively reacts to insulate impact and vibration in comparison with the front bushing connected to the powertrain. Therefore, a number of efforts have been made to improve performance of the roll rod by developing the rear bushing in the art.
That is, because a rod portion of a structure of the roll rod has a predetermined length and is positioned at a lowest end of the vehicle, there is great concern that the rod portion will be damaged due to external factors, and as a result, the roll rod is generally made of aluminum or steel. In addition, at the time of a sudden unintended acceleration evaluation, the engine mount and the transmission mount support force at an upper end, but at a lower end, the rear roll rod supports the resultant force of the two mounts, and as a result, a significantly high load is applied to the rod portion.
Therefore, the rod portion is an important portion in respect to reducing weights and costs and ensuring strength and rigidity when the rod portion of the roll rod is manufactured, and as a result, a squeeze process method, which has long cycle timing and makes it easy to ensure strength and rigidity, is generally used. However, the squeeze process method is very disadvantageous in terms of costs, and as a result, there is a need for a structure which is excellent in respect to improving cost efficiency as well as strength and rigidity.
The following patent literature is related to subject matter disclosed herein: Korean Patent Application Laid-Open No. 10-2007-0060401 (Jun. 13, 2007).
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.